1. Field of the Invention
This invention relates to deflector devices of the kind used between a towing vessel and a tow located in water, for example a seismic streamer or streamer array, or a seismic source array, in order to pull the tow out to one side of the vessel, so as to position it at a desired lateral offset from the course followed by the vessel.
2. Description of the Related Art
A deflector device of this kind is described in detail in our U.S. Pat. No. 5,357,892, and comprises a wing-shaped deflector body having a remotely-operable pivotal lever or “boom” which extends rearwardly from a point near the middle of the trailing edge of the wing-shaped body. In use, the wing-shaped deflector body is suspended beneath a float so as to be completely submerged and positioned generally vertically in the water, and is connected to the towing vessel by means of a tow line, while the tow is connected to the end of the boom remote from the wing-shaped body. As the device is pulled through the water, the wing-shaped body produces a sideways force, or “lift”, which moves the tow laterally. This lift can be varied by adjusting the angle of the boom from the vessel, thus permitting the lateral offset of the tow from the course of the vessel to be varied in use.
The deflector device of U.S. Pat. No. 5,357,892 has been successfully commercialised by the Applicant as its MONOWING deflector device. In use, rolling stability of the device is provided by the connection to the float, while stability of the device about a vertical axis is provided by the drag produced by the tow.
The deflectors in current use are very large, typically 7.5 m high by 2.5 m wide, and weigh several tonnes. They are usually suspended around 2 m to 8 m below the float by means of a fibre rope, and are also provided with a safety chain intended to prevent separation of the float and deflector wing in the event that the rope breaks.
In bad weather, the upper part of the deflector wing may rise up out of the water, allowing the rope connecting the deflector wing and the float to go slack. If the deflector wing then drops abruptly, the rope, and possibly the safety chain, may break, and/or the attachment points may be damaged.
One solution to this problem is disclosed in PCT Patent Application No. PCT/IB98/01946 (WO 99/33700). It is an object of the present invention to provide an alternative and simpler solution.